Air-tight passive houses, especially those that leak merely <200cfm (in our case < 0.2 ACH50), present a number of challenges when it comes to appliance selection. The two appliances that must be carefully selected are cooking vents/hoods and clothes dryers (or tumble dryers).

At only ~200cfm leakage, operating a venting dryer can depressurize such a home and may cause strain on the clothes dryer motor as they typically vent to the outside at about 150cfm or so. Further more, vented dryers penetrate the air-tight building envelope.

The are specialized vents that claim to minimize air-leakage, but they may only be effective during negative pressurization as they are designed to open their valves when positively pressurized (by exhaust air from the dryer itself).

One could also, I suppose, create some sort of operating mechanism that could be configured to open and close solidly, but that would require a temperature controlled trigger or manual closing and opening.

Clothing drying cabinet

Another alternative to clothes drying is the use of a drying cabinet or closet. Such things are fairly popular abroad, especially in a passivhaus.

It is entirely plausible to use a clothes line outside (like my mother used to do when I was a kid). Clothes dried in this fashion tend to dry out really fresh smelling and soft, too. But they can also be unsightly.

Today, in the U.S., most of us are accustomed to using a clothes dryer.

So what are we to do?

Fortunately solutions do exist to address this conundrum. Ventless condensing dryers are available to address this need. They can often be found in apartment buildings where access to a dryer vent is not possible.

In the case of a ventless condensing dryer, cold water is passes by the internal heated and moist air which causes the air mixture to condense. This condensed water is then drained away either into a water container or, better yet, into a plumbing drain line.

While capacities tend to be quite a bit smaller than full-sized dryers they tend to have extended drying cycles. One of the advantages of using a condensing dryer is that they can be placed in just about any room in the home as they do not require connect to a dryer vent.

A variation of a condensing dryer, is a washer dryer combo unit that does both washing and drying functions. It is common that these appliances operate with merely 115-120 volts as opposed to 220-240v. Their entire cycle also tend to consume little energy relative to conventional washers and dryers.

Abroad there exists variations of condensing dryers that have yet to make their way to our shoreline. These units generate their heat with a heat-pump system (similar to what heat-pump hot water heaters do). These units can produce heat with COPs greater than one as opposed to conventional electric heating elements that only generate 3.4 Btu/watt (at a COP of only one).

These appliances are more complicated and may be subject to more frequent break-downs given their increased complexity. Additionally, they can be quite a bit more expensive than condensing dryers which utilize conventional heating elements.

In our case we have used German-made (imagine that) Miele appliances throughout our home.

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